package thread;

import java.util.Map;
import java.util.TreeMap;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class RWDictionary {
	private final Map<String,String> m = new TreeMap<String,String>();
	private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
	private final Lock r = rwl.readLock();
	private final Lock w = rwl.writeLock();
	public String get(String key){
		r.lock();
		try {
			return m.get(key);
		} finally  {
			r.unlock();
		}
	}
	public String[] allKeys()	{
		r.lock();
		try{
			return m.keySet().toArray(new String[1]);
		}finally{
			r.unlock();
		}
	}
	public String put(String key,String value){
		w.lock();
		try{
			return m.put(key, value);
		}finally{
			w.unlock();
		}
	}
	public void clear(){
		w.lock();
		try{
			m.clear();
		}finally{
			w.unlock();
		}
	}
}
